1. Field of the Invention
The present invention relates to a steering apparatus including a telescopic adjusting mechanism and an impact absorbing mechanism for a secondary collision and allowing the mechanisms to be shared by the same member, the steering apparatus further allowing a telescopic holding operation and an impact absorbing operation to be performed independently so as not to affect each other.
2. Description of the Related Art
Various steering apparatuses are present which include a telescopic adjusting mechanism and an impact absorbing apparatus configured to protect a driver at the time of a secondary collision when a collision accident occurs. As one common structure of a steering apparatus of this kind, a conventional technique is disclosed in which, at the time of a secondary collision, a bracket moves along a slot against the pressing force of a clamping bolt.
Furthermore, an effect is conventionally used in which the slot in the bracket is formed to be smaller than the diameter of the clamping bolt so that, when a predetermined load acts on the bracket, the bracket moves while the edge of the slot is being collapsed by the clamping bolt. One of such conventional techniques as illustrated above is disclosed in Japanese Patent Application Laid-open No. 2002-337699.
Japanese Patent Application Laid-open No. 2002-337699 will be described in brief. To be distinguished from the description of the present invention, the description of Japanese Patent Application Laid-open No. 2002-337699 uses parenthesized reference numerals. A steering apparatus in Japanese Patent Application Laid-open No. 2002-337699 has a second upper bracket (22) welded to a column (2) at an upper end of the second upper bracket (22) and which moves in conjunction with the column relative to a vehicle body when the column (2) moves relative to the vehicle body as a result of an impact.
Furthermore, the second upper bracket (22) is sandwiched between opposite walls (21a and 21b) of a first upper bracket (21) fixed to the vehicle body so as to be slidable relative to the vehicle body. Threaded shafts (51) with heads (51′) with lateral axes are inserted in first through-holes (41) formed in the opposite sidewalls (21a and 21b) of the first upper bracket (21) and in second through-holes (42) formed in opposite sidewalls (22a and 22b) of the second upper bracket (22). The threaded shaft (51) has a nut (54) screw threaded over the shaft (51) via a washer (52) and a lever (53) integrated with the nut (54).
In Japanese Patent Application Laid-open No. 2002-337699, when clamping is performed using the levers of the threaded shafts (51) with the heads (51)′, the opposite sidewalls (22a and 22b) of the second upper bracket (22) with a telescopic adjusting section and an energy absorbing section formed thereon come into pressure contact with the opposite sidewalls (22a and 22b) of the first upper bracket (21). That is, the opposite sidewalls (22a and 22b) of the second upper bracket 22 serve as surfaces fractioned against the opposite sidewalls (21a and 21b) of the first upper bracket (21).
In other words, both the telescopic adjusting section and the energy absorbing section are used by a single member. Thus, in a clamped (locked) state following completion of telescopic adjustment, the second upper bracket (22) is subjected to a sandwiching pressure from the first upper bracket (21).
Thus, an energy absorbing operation in Japanese Patent Application Laid-open No. 2002-337699 definitely involves not only a structure in which “the impact is absorbed based on the advancement of the threaded shaft (51) from a shaft standby area (42b) into an impact absorbing area (42a), which pushes the second through-hole (42) open to plastically deform the second upper bracket (22)” but also the sandwiching pressure from the first upper bracket (21) as described above. In other words, the sandwiching pressure from the first upper bracket (21) sandwiching the second upper bracket (22) between the sidewalls has a significant effect on the operation of absorbing an impact load at the time of a secondary collision.
In these circumstances, in setting of the load of impact absorption at the time of a secondary collision, it is necessary to sufficiently consider a frictional load on the frictional surface resulting from the sandwiching pressure from the first upper bracket (21) as well as resistance offered to the threaded shaft (51) by the impact absorbing area (42a) during relative movement. Thus, setting the energy absorbing load is extremely difficult.
Furthermore, in Japanese Patent Application Laid-open No. 2002-337699, at the time of impact absorption, the threaded shaft (51) moves from the shaft standby area (42b) into the impact absorbing area (42a) in such a way as to push the impact absorbing area (42a) open, thus plastically deforming the second upper bracket (22). A portion collapsed in the plastically deformed area may stick out between the lateral sidewalls (21a and 21b) of the first upper bracket (21) and the lateral sidewalls (22a and 22b) of the second upper bracket (22). When the sticking-out portion is rubbed against the frictional surface, the impact absorbing load increases. The shape, amount, direction, and the like of the portion sticking out due to plasticity vary depending on the impact. Thus, controlling the energy absorbing load with the effect on the frictional surface taken into account is difficult. Hence, setting the desired energy absorbing load is difficult.
An object of the present invention (a technical problem to be solved by the invention) is to provide a steering apparatus which includes a telescopic adjusting mechanism and an impact absorbing mechanism for a secondary collision and which allows these mechanisms to be shared by the same member, the steering apparatus preventing a telescopic holding operation and an impact absorbing operation from affecting each other.